ABSTRACT
Open clusters are relatively young and numerous. These systems are distributed throughout the Galactic disc and provide insights on the chemistry of the Milky Way. In this study, we provide ...a near-infrared spectroscopic analysis of four stars of the young open cluster NGC 2345. Our infrared data present a resolving power of R ≈ 45 000, covering the H- and K-bands (1.5–2.5 μm), and high-signal-to-noise ratio, which are gathered with the Immersion Grating Infrared Spectrograph (IGRINS) at the Gemini Observatory. From atmospheric parameters previously derived via optical spectroscopy, we obtain abundances for C (12C16O), N (12C14N), O (16OH), F (H19F), Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, Cr, Fe, Ni, Ce, Nd, and Yb. Additionally, the 12C/13C (13C16O), 16O/17O (12C17O), and 16O/18O (12C18O) isotopic ratios are obtained. We compare the infrared results with a previous work based on optical spectral analysis, but chemical species such as F, S, P, K, and Yb are determined for the first time in stars of NGC 2345. We also confirm a low metallicity (Fe/H = −0.32 ± 0.04) and slight enrichment in s-process elements, as already noticed in works available in the literature, but we do not find any enrichment in F. Our results demonstrate excellent agreement between our measured isotopic ratios 12C/13C and 16C/17O and models of stellar nucleosynthesis, while we find that the abundance of 18O is overestimated in comparison to our measurements. Finally, we assess our findings in comparison to the chemical patterns observed in open clusters, classified by both their age and Galactocentric distances, and highlight the need for a more comprehensive sample of young clusters within the 9–11 kpc range for a proper comparison.
Abstract This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of ∼2000 stars in the Galactic bulge bar ...spatially contained within ∣ X Gal ∣ < 5 kpc, ∣ Y Gal ∣ < 3.5 kpc, and ∣ Z Gal ∣ < 1 kpc, and spanning metallicities between −2.0 ≲ Fe/H ≲ +0.5. We classify the sample stars into low- or high-Mg/Fe populations and find that, in general, values of Ce/Fe and Nd/Fe increase as the metallicity decreases for the low- and high-Mg/Fe populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r -process dominating the production of neutron-capture elements in the high-Mg/Fe population (Ce/Nd < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-Mg/Fe populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-Mg/Fe population is dominated by stars with low Ce/Fe, Ce/Mg, Nd/Mg, Nd/Fe, and Ce/Nd ratios. The low Ce/Nd ratio indicates a significant contribution in this central region from r -process yields for the low-Mg/Fe population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r -process astrophysical sites, such as magnetorotational supernovae.
Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the ...Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk. Aims. Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4−15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk. Methods. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances. Results. Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800−31 300 K, and surface gravities between 3.23−4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of −0.07 dex kpc−1 and −0.09 dex kpc−1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc. Conclusions. The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane.
ABSTRACT
Binary interactions play a significant role in stellar evolution. In this study, we present a comprehensive analysis of 17 single-lined spectroscopic binary stars and identify two more as ...‘yellow stragglers’, in the context of 15 young open clusters with ages younger than 1.0 Gyr. High-resolution spectroscopy ($R\, \approx \, 48000$) was employed to determine atmospheric parameters and chemical abundances of various elements including Li, C (C2), N (12CN), O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, Nd, and Eu, and compared them with the abundances of stars reported in the literature. The projected rotational velocities ($v\, \sin \, \mathrm{ i}$) of 17 stars were determined via the spectral synthesis method. For two stars, we analyse the phenomenon of yellow stragglers based on their spectra and colour–magnitude diagram. Our $v\, \sin \, \mathrm{ i}$ results exhibit excellent agreement with previous studies in the literature for four stars previously analysed. Furthermore, we found a similar set of chemical abundances between thin disc stars and the studied spectroscopic binaries, except for s-process elements, such as La, Ce, and Nd. Also, we confirm that yellow straggler stars are members of binary systems, specifically giant G/K-type stars paired with dwarf A-type stars. Finally, we investigated the relationships between chemical abundances, orbital parameters (obtained from the literature), and $v\, \sin \, \mathrm{ i}$, which can provide insights into the observed anomalies in 7Li abundance in two stars such as NGC 6694-14 and NGC 6709-303. Our findings suggest that the anomalous rotation and lithium enrichment observed in these stars are likely results of interactions within binary companions.
ABSTRACT
In general, the atypical high velocity of some stars in the Galaxy can only be explained by invoking acceleration mechanisms related to extreme astrophysical events in the Milky Way. Using ...astrometric data from Gaia and the photometric information in 12 filters of the S-PLUS, we performed a kinematic, dynamical, and chemical analysis of 64 stars with Galactocentric velocities higher than 400 $\mathrm{km\, s}^{-1}$. All the stars are gravitationally bound to the Galaxy and exhibit halo kinematics. Some of the stars could be remnants of structures such as the Sequoia and the Gaia-Sausage/Enceladus. Supported by orbital and chemical analysis, we identified Gaia DR3 5401875170994688896 as a star likely to be originated at the centre of the Galaxy. Application of a machine learning technique to the S-PLUS photometric data allows us to obtain very good estimates of magnesium abundances for this sample of high-velocity stars.
Abstract
The APOGEE Open Cluster Chemical Abundances and Mapping survey is used to probe the chemical evolution of the s-process element cerium in the Galactic disk. Cerium abundances were derived ...from measurements of Ce
ii
lines in the APOGEE spectra using the Brussels Automatic Code for Characterizing High Accuracy Spectra in 218 stars belonging to 42 open clusters. Our results indicate that, in general, for ages < 4 Gyr, younger open clusters have higher Ce/Fe and Ce/
α
-element ratios than older clusters. In addition, metallicity segregates open clusters in the Ce/X–age plane (where X can be H, Fe, or the
α
-elements O, Mg, Si, or Ca). These metallicity-dependent relations result in Ce/Fe and Ce/
α
ratios with ages that are not universal clocks. Radial gradients of Ce/H and Ce/Fe ratios in open clusters, binned by age, were derived for the first time, with
d
Ce/H/
d
R
GC
being negative, while
d
Ce/Fe/
d
R
GC
is positive. Ce/H and Ce/Fe gradients are approximately constant over time, with the Ce/Fe gradient becoming slightly steeper, changing by ∼+0.009 dex kpc
−1
Gyr
−1
. Both the Ce/H and Ce/Fe gradients are shifted to lower values of Ce/H and Ce/Fe for older open clusters. The chemical pattern of Ce in open clusters across the Galactic disk is discussed within the context of s-process yields from asymptotic giant branch (AGB) stars, gigayear time delays in Ce enrichment of the interstellar medium, and the strong dependence of Ce nucleosynthesis on the metallicity of its AGB stellar sources.
Aims.
We estimated the spectral evolution of white dwarfs with effective temperature using the Javalambre Photometric Local Universe Survey (J-PLUS) second data release (DR2), which provides 12 ...photometric optical passbands over 2176 deg
2
.
Methods.
We analyzed 5926 white dwarfs with
r
≤ 19.5 mag in common between a white dwarf catalog defined from
Gaia
EDR3 and J-PLUS DR2. We performed a Bayesian analysis by comparing the observed J-PLUS photometry with theoretical models of hydrogen- and helium-dominated atmospheres. We estimated the probability distribution functions for effective temperature (
T
eff
), surface gravity, parallax, and composition; and the probability of having a H-dominated atmosphere (
p
H
) for each source. We applied a prior in parallax, using
Gaia
EDR3 measurements as a reference, and derived a self-consistent prior for the atmospheric composition as a function of
T
eff
.
Results.
We described the fraction of white dwarfs with a He-dominated atmosphere (
f
He
) with a linear function of the effective temperature at 5000 <
T
eff
< 30 000 K. We find
f
He
= 0.24 ± 0.01 at
T
eff
= 10 000 K, a change rate along the cooling sequence of 0.14 ± 0.02 per 10 kK, and a minimum He-dominated fraction of 0.08 ± 0.02 at the high-temperature end. We tested the obtained
p
H
by comparison with spectroscopic classifications, finding that it is reliable. We estimated the mass distribution for the 351 sources with distance
d
< 100 pc, mass
M
> 0.45
M
⊙
, and
T
eff
> 6000 K. The result for H-dominated white dwarfs agrees with previous studies, with a dominant
M
= 0.59
M
⊙
peak and the presence of an excess at
M
∼ 0.8
M
⊙
. This high-mass excess is absent in the He-dominated distribution, which presents a single peak.
Conclusions.
The J-PLUS optical data provide a reliable statistical classification of white dwarfs into H- and He-dominated atmospheres. We find a 21 ± 3% increase in the fraction of He-dominated white dwarfs from
T
eff
= 20 000 K to
T
eff
= 5000 K.
Context. We present a new methodology for the estimation of stellar atmospheric parameters from narrow- and intermediate-band photometry of the Javalambre Photometric Local Universe Survey (J-PLUS), ...and propose a method for target pre-selection of low-metallicity stars for follow-up spectroscopic studies. Photometric metallicity estimates for stars in the globular cluster M15 are determined using this method. Aims. By development of a neural-network-based photometry pipeline, we aim to produce estimates of effective temperature, Teff, and metallicity, Fe/H, for a large subset of stars in the J-PLUS footprint. Methods. The Stellar Photometric Index Network Explorer, SPHINX, was developed to produce estimates of Teff and Fe/H, after training on a combination of J-PLUS photometric inputs and synthetic magnitudes computed for medium-resolution (R ~ 2000) spectra of the Sloan Digital Sky Survey. This methodology was applied to J-PLUS photometry of the globular cluster M15. Results. Effective temperature estimates made with J-PLUS Early Data Release photometry exhibit low scatter, σ(Teff) = 91 K, over the temperature range 4500 < Teff (K) < 8500. For stars from the J-PLUS First Data Release with 4500 < Teff (K) < 6200, 85 ± 3% of stars known to have Fe/H < −2.0 are recovered by SPHINX. A mean metallicity of Fe/H = − 2.32 ± 0.01, with a residual spread of 0.3 dex, is determined for M15 using J-PLUS photometry of 664 likely cluster members. Conclusions. We confirm the performance of SPHINX within the ranges specified, and verify its utility as a stand-alone tool for photometric estimation of effective temperature and metallicity, and for pre-selection of metal-poor spectroscopic targets.
High-velocity Stars in SDSS/APOGEE DR17 Quispe-Huaynasi, F.; Roig, F.; McDonald, D. J. ...
The Astronomical journal,
11/2022, Letnik:
164, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Abstract
We report 23 stars having Galactocentric velocities larger than 450 km s
−1
in the final data release of the APOGEE survey. This sample was generated using space velocities derived by ...complementing the high-quality radial velocities from the APOGEE project in Sloan Digital Sky Survey’s Data Release 17 (DR17) with distances and proper motions from Gaia early Data Release 3 (eDR3). We analyze the observed kinematics and derived dynamics of these stars, considering different potential models for the Galaxy. We find that three stars could be unbound depending on the adopted potential, but in general all of the stars show typical kinematics of halo stars. The APOGEE DR17 spectroscopic results and Gaia eDR3 photometry are used to assess the stellar parameters and chemical properties of the stars. All of the stars belong to the red giant branch, and, in general, they follow the abundance pattern of typical halo stars. There are a few exceptions that would deserve further analysis through high-resolution spectroscopy. In particular, we identify a high-velocity Carbon-Enhanced Metal-Poor star, with a Galactocentric velocity of 482 km s
−1
. We do not confirm any hypervelocity star in the sample, but this result is very sensitive to the adopted distances and less sensitive to the Galactic potential.
Aims.
We present the photometric calibration of the twelve optical passbands for the Javalambre Photometric Local Universe Survey (J-PLUS) second data release (DR2), comprising 1088 pointings of two ...square degrees, and study the systematic impact of metallicity on the stellar locus technique.
Methods.
The Fe/H metallicity from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) for 146 184 high-quality calibration stars, defined with signal-to-noise ratio larger than ten in J-PLUS passbands and larger than three in
Gaia
parallax, was used to compute the metallicity-dependent stellar locus (ZSL). The initial homogenization of J-PLUS photometry, performed with a unique stellar locus, was refined by including the metallicity effect in colors via the ZSL.
Results.
The variation of the average metallicity along the Milky Way produces a systematic offset in J-PLUS calibration. This effect is well above 1% for the bluer passbands and amounts 0.07, 0.07, 0.05, 0.03, and 0.02 mag in
u
,
J
0378,
J
0395,
J
0410, and
J
0430, respectively. We modeled this effect with the Milky Way location of the J-PLUS pointing, also providing an updated calibration for those observations without LAMOST information. The estimated accuracy in the calibration after including the metallicity effect is at 1% for the bluer J-PLUS passbands and below for the rest.
Conclusions.
Photometric calibration with the stellar locus technique is prone to significant systematic bias in the Milky Way for passbands bluer than
λ
= 4500 Å. The calibration method for J-PLUS DR2 reaches 1–2% precision and 1% accuracy for 12 optical filters within an area of 2176 square degrees.
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